Onomatopoeia

Linguists are now agreed that the
vast majority of words in every language are entirely arbitrary,
but a small class of signifiers
somehow mimic their signifieds. Examples include "thud,"
"screech," "bark" (the sound a dog makes, not tree-skin), "pop,"
and so on. (Of course these words vary from language to
language, so the mimicry isn't perfect.) Sometimes poetry can
use words which, through their very sound, suggest their
subject.